In situ thermal processing of a coal formation using a controlled heating rate

Abstract

A coal formation may be treated using an in situ thermal process. A mixture of hydrocarbons, H 2 , and/or other formation fluids may be produced from the formation. Heat may be applied to the formation to raise a temperature of a portion of the formation to a pyrolysis temperature. A heating rate to a selected volume of the formation may be controlled by altering an amount of heating energy per day that is provided to the selected volume.

What is claimed is:  
     
       1. A method or treating a coal formation in situ, comprising: 
       healing a selected volume (V) of the coal formation, wherein the formation has an average heat capacity (C v ), and wherein the heating pyrolyzes at least some hydrocarbons in the selected volume of the formation;  
       wherein heating energy/day (Pwr) provided to the selected volume is equal to or less than h*V*C v *ρ B , wherein ρ B  is formation bulk density, and wherein an average heating rate (h) of the selected volume is about 10° C./day; and  
       producing a mixture from the formation.  
     
     
       2. The method of  claim 1 , wherein heating the selected volume comprises heating with at least one electrical heater. 
     
     
       3. The method of  claim 1 , wherein heating the selected volume comprises heating with at least one surface burner. 
     
     
       4. The method or  claim 1 , wherein heating the selected volume comprises heating with at least one flameless distributed combustor. 
     
     
       5. The method of  claim 1 , wherein heating the selected volume comprises heating with at least one natural distributed combustor. 
     
     
       6. The method of  claim 1 , further comprising controlling a pressure and a temperature in at least a majority of the selected volume of the formation, wherein the pressure is controlled as a function of temperature, or the temperature is controlled as a function of pressure. 
     
     
       7. The method of  claim 1 , wherein a value for C v  is determined as an average heat capacity of two or more samples taken from the coal formation. 
     
     
       8. The method of  claim 1 , wherein heating the selected volume comprises transferring heat substantially by conduction. 
     
     
       9. The method of  claim 1 , wherein heating the selected volume increases a thermal conductivity of at least a portion of the selected volume to greater than about 0.5 W/(m ° C.). 
     
     
       10. The method of  claim 1 , wherein the produced mixture comprises condensable hydrocarbons having an API gravity of at least about 25°. 
     
     
       11. The method of  claim 1 , wherein the produced mixture comprises condensable hydrocarbons, and wherein about 0.1% by weight to about 15% by weight of the condensable hydrocarbons are olefins. 
     
     
       12. The method of  claim 1 , wherein the produced mixture comprises non-condensable hydrocarbons, and wherein about 0.1% by weight to about 15% by weight of the non-condensable hydrocarbons are olefins. 
     
     
       13. The method of  claim 1 , wherein the produced mixture comprises non-condensable hydrocarbons, and wherein a molar ratio of ethene to ethane in the non-condensable hydrocarbons ranges from about 0.001 to about 0.15. 
     
     
       14. The method of  claim 1 , wherein the produced mixture comprises condensable hydrocarbons, and wherein less than about 1% by weight, when calculated on an atomic basis, of the condensable hydrocarbons is nitrogen. 
     
     
       15. The method of  claim 1 , wherein the produced mixture comprises condensable hydrocarbons, and wherein less than about 1% by weight, when calculated on an atomic basis, of the condensable hydrocarbons is oxygen. 
     
     
       16. The method of  claim 1 , wherein the produced mixture comprises condensable hydrocarbons, wherein about 5% by weight to about 30% by weight of the condensable hydrocarbons comprise oxygen containing compounds, and wherein the oxygen containing compounds comprise phenols. 
     
     
       17. The method of  claim 1 , wherein the produced mixture comprises condensable hydrocarbons, and wherein greater than about 20% by weight of the condensable hydrocarbons are aromatic compounds. 
     
     
       18. The method of  claim 1 , wherein the produced mixture comprises condensable hydrocarbons, and wherein less than about 5% by weight of the condensable hydrocarbons comprises multi-ring aromatics with more than two rings. 
     
     
       19. The method of  claim 1 , wherein the produced mixture comprises condensable hydrocarbons, and wherein less than about 0.3% by weight of the condensable hydrocarbons are asphaltenes. 
     
     
       20. The method of  claim 1 , wherein the produced mixture comprises condensable hydrocarbons, and wherein about 5% by weight to about 30% by weight of the condensable hydrocarbons are cycloalkanes. 
     
     
       21. The method of  claim 1 , wherein the produced mixture comprises a non-condensable component, wherein the non-condensable component comprises molecular hydrogen, wherein the molecular hydrogen is greater than about 10% by volume of the non-condensable component at 25° C. and one atmosphere absolute pressure, and wherein the molecular hydrogen is less than about 80% by volume of the non-condensable component at 25° C. and one atmosphere absolute pressure. 
     
     
       22. The method of  claim 1 , wherein the produced mixture comprises ammonia, and wherein greater than about 0.05% by weight of the produced mixture is ammonia. 
     
     
       23. The method of  claim 1 , wherein the produced mixture comprises ammonia, and wherein the ammonia is used to produce fertilizer. 
     
     
       24. The method of  claim 1 , further comprising controlling a pressure in at least a majority of the selected volume of the formation, wherein the controlled pressure is at least about 2.0 bars absolute. 
     
     
       25. The method of  claim 1 , further comprising controlling formation conditions to produce the mixture, wherein a partial pressure of H 2  in the mixture is greater than about 0.5 bar. 
     
     
       26. The method of  claim 25 , wherein the partial pressure of H 2  in the mixture is determined based on production well conditions. 
     
     
       27. The method of  claim 1 , further comprising recirculating a portion of hydrogen from the mixture into the formation. 
     
     
       28. The method of  claim 1 , further comprising: 
       providing hydrogen (H 2 ) to the selected volume of the formation to hydrogenate hydrocarbons in the selected volume; and  
       heating a portion of the selected volume with heat from hydrogenation.  
     
     
       29. The method of  claim 1 , further comprising: 
       producing hydrogen and condensable hydrocarbons from the formation; and  
       hydrogenating a portion of the produced condensable hydrocarbons with at least a portion of the produced hydrogen.  
     
     
       30. The method of  claim 1 , wherein heating the selected volume of the formation increases a permeability of a majority of tine selected volume to greater than about 100 millidarcy. 
     
     
       31. The method of  claim 1 , wherein heating the selected volume of the formation increases a permeability of a majority of the selected volume such that the permeability of the majority of the selected volume is substantially uniform. 
     
     
       32. The method of  claim 1 , further comprising controlling the heat to yield greater than about 60% by weight of condensable hydrocarbons, as measured by Fischer Assay. 
     
     
       33. The method of  claim 1 , wherein producing the mixture comprises producing the mixture in a production well, and wherein at least about 7 heaters are disposed in the formation for catch production well. 
     
     
       34. The method of  claim 1 , further comprising providing heat from three or more heaters to at least a portion of the formation, wherein three or more of the heaters are located in the formation in a unit of heaters, and wherein the unit of heaters comprises a triangular pattern. 
     
     
       35. The method of  claim 1 , further comprising providing heat from three or more heaters to at least a portion of the formation, wherein three or more of the heaters are located in the formation in a unit of heaters, wherein the unit of heaters comprises a triangular pattern, and wherein a plurality of the units tire repeated over an area of the formation to form a repetitive patient of units. 
     
     
       36. A method of treating a coal formation in situ, comprising: 
       calculating a heating energy/day (Pwr) to heat a selected volume (V) of the coal formation, wherein the coal formation has an average heat capacity (C v ) and a bulk density (ρ B ), wherein the heating energy/day (Pwr) is calculated to be equal to or less than h*V*C v *ρ B , wherein an average heating rate (h) is about 10° C./day; and  
       heating the selected volume by providing the calculated heating energy/day (Pwr) or less than the calculated heating energy/day (Pwr) to the selected volume to pyrolyze at least some hydrocarbons in the selected volume.  
     
     
       37. The method of  claim 36 , wherein heating the selected volume comprises heating the selected volume with at least one natural distributed combustor. 
     
     
       38. The method of  claim 36 , wherein a value for C v  is determined as an average heat capacity of two or more samples taken from the coal formation. 
     
     
       39. The method of  claim 36 , wherein heating the selected volume raises the thermal conductivity of at least a portion of the selected volume to a value greater than about 0.5 W/(m ° C.). 
     
     
       40. A method of treating a coal formation in situ, comprising: 
       calculating a heating energy/day (Pwr) to heat a selected volume (V) of the coal formation, wherein the coal formation has an average heat capacity (C v ) and a bulk density (ρ B ), wherein the heating energy/day (Pwr) is calculated to be equal to or less than h*V*C v *ρ B , wherein an average heating rate (h) is about 10° C./day; and  
       providing heat from one or more heaters to the selected volume by providing the calculated heating energy/day (Pwr) or less than the calculated heating energy/day (Pwr) to the selected volume to pyrolyze at least some hydrocarbons in the selected volume.  
     
     
       41. The method of  claim 40 , wherein at least one of the heaters comprises a natural distributed combustor. 
     
     
       42. The method of  claim 40 , wherein a value for C v  is determined as an average heat capacity of two or more samples taken from the coal formation. 
     
     
       43. The method of  claim 40 , wherein heating the selected volume raises the thermal conductivity of at least a portion of the selected volume to a value greater than about 0.5 W/(m ° C).